Plant growth regulators induce differential responses on primary and specialized metabolism of Annona emarginata (Annonaceae)

Plants belonging to the Annonaceae family are known to produce several specialized metabolites, including alkaloids and volatiles of pharmacological interest. However, there are no reports on how specialized metabolism (SM) can respond to the exogenous application of plant regulators and how this possible modulation is associated with primary metabolism (PM). Thus, the aim of this work was to evaluate SM and PM responses of Annona emarginata as a function of the application of plant growth regulators. For this, young plants were treated with auxin, methyl jasmonate, salicylic acid and abscisic acid at various concentrations. To know the particular effect of auxin, a second experiment was carried out using auxin and its inhibitor, observing responses at various times after application. SM responses were the quantification of total alkaloids, oxoaporphine liriodenine, number of alkaloids in roots and leaf volatile profile. For PM, gas exchange and chlorophyll a fluorescence variables were determined. Some plant regulators promoted changes over photosynthesis variables in Annona emarginata at specific concentrations and evaluation times; the most pronounced effects were caused by auxin, mainly reduction in net carbon assimilation and less photochemical dissipation at 10-6 M. The application of 10-6 M auxin and 10-3 M salicylic acid in A. emarginata caused increase in total alkaloids and liriodenine. All regulators altered the composition of leaf volatiles, that were reflected in the classes of volatiles or in individual molecules, for example, with auxin, methyl jasmonate and salicylic acid decreasing the relative proportion of monoterpenes, and abscisic acid causing alterations in sesquiterpenes. Thus, it was possible to demonstrate that A. emarginata alters the energy flow between primary and specialized metabolism as a function of the applied plant regulator and that the number and proportion of specialized metabolites are modulated according to the applied plant regulator.